Cryogenic cooling device and method

ABSTRACT

Cryogenic cooling method and device comprising a main cryogenic cooler comprising a cold head positioned in a first chamber selectively placed under vacuum, a reservoir of working fluid placed in a second chamber selectively placed under vacuum, a member to be cooled being placed in the reservoir in heat exchange with the working fluid, the cold head of the main cryogenic cooler being thermally connected to a heat exchanger which is itself fluidically connected to the reservoir via pipes forming a first circulation loop for the working fluid, the pipes passing from the first to the second chamber, characterized in that the volumes selectively under vacuum of the first and second chambers are independent and in that the device comprises a secondary cryogenic cooler comprising a cold head placed in a third chamber selectively placed under vacuum, the cold head of the secondary cryogenic cooler being thermally connected to a heat exchanger which is itself fluidically connected to the reservoir via pipes forming a second circulation loop for the working fluid, and in that the volume selectively under vacuum of the third chamber is independent of the volumes selectively under vacuum of the first and second chambers.

The present invention relates to a cryogenic cooling device and method.

It should be noted that the work leading up to the present invention enjoyed funding from the European Union 7^(th) framework program FP/2007-2013 under grant No. 241285.

The invention relates more particularly to a cryogenic cooling device comprising a main cryocooler with a cold head arranged in a first chamber selectively placed under vacuum, a reservoir of working fluid arranged in a second chamber selectively placed under vacuum, a member that is to be cooled being arranged in the reservoir in a heat exchange relationship with the working fluid, the cold head of the main cryocooler being thermally connected to a heat exchanger, itself fluidically connected to the reservoir via pipes forming a first circulation loop for the working fluid, the pipes passing from the first to the second chamber.

Document US20090049862A1 describes a refrigeration device using a cryocooler to liquefy a working fluid, for example nitrogen. The liquefied working fluid is used in the conventional way to cool an application to a very low temperature, typically superconductor cables.

In sensitive electrical applications, this type of cooler has to be able to operate uninterrupted. However, the known solutions do not allow the refrigeration device to undergo maintenance or repair in a way that is simple and easy for an operator and minimizes the impact on the production of cold.

It is an object of the present invention to alleviate all or some of the abovementioned disadvantages of the prior art.

To this end, the device according to the invention, which in other respects is in accordance with the generic definition thereof given in the above preamble, is essentially characterized in that the volumes selectively under vacuum of the first and second chambers are independent and in that the device comprises a secondary cryocooler comprising a cold head arranged in a third chamber selectively placed under vacuum, the cold head of the secondary cryocooler being thermally connected to a heat exchanger, itself fluidically connected to the reservoir via pipes forming a second circulation loop for the working fluid, and in that the volume selectively under vacuum of the third chamber is independent of the volumes selectively under vacuum of the first and second chambers.

Furthermore, some embodiments of the invention may include one or more of the following features:

-   -   out of the first and third chambers, at least one is sealed off         by at least one selectively removable cap;     -   at least one selectively removable cap is arranged in the lower         part of the chamber such that it is adjacent to the cold head;     -   at least one cap is mounted in a sealed fashion on the body of         the chamber via fixing screws;     -   the device comprises, around the pipes passing from the first to         the second chamber, vacuum barriers which separate the volumes         selectively under vacuum of the first and second chambers, the         vacuum barriers being arranged in at least one tubular portion         that connects the first and second chambers;     -   the device comprises, around the pipes passing from the third to         the second chamber, vacuum barriers which separate the volumes         selectively under vacuum of the third and second chambers, the         vacuum barriers being arranged in at least one tubular portion         that connects the third and second chambers;     -   the cold head of the cryocooler(s) is associated with a heat         exchanger that acts as a condenser for the working fluid;     -   the cold head of the main cryocooler is connected to the         reservoir via two pipes the upstream ends of which are connected         to a hermetic volume arranged under the cold head of the main         cryocooler, the downstream ends of the pipes being connected to         an upper end of the reservoir via a vertical or substantially         vertical portion;     -   the cold head of the secondary cryocooler is connected to the         reservoir via two pipes the upstream ends of which are connected         to a hermetic volume arranged under the cold head of the         secondary cryocooler and the downstream ends of which are         connected to an upper end of the reservoir via a vertical or         substantially vertical portion;     -   in the operating configuration, out of: the main cryocooler and         the secondary cryocooler, at least one is arranged in a vertical         configuration,     -   the vacuum barriers comprise for example at least one of the         following members: a system referred to as a “simple cone”         system, a system referred to as a “double cone” system,     -   a heater, for example an electric heater, is mounted on at least         one heat exchanger of a cold head of a cryocooler,     -   the chamber or chambers are placed under vacuum with respect to         air at a pressure of between 10⁻³ and 10⁻⁶ mbar,     -   the member that is to be cooled comprises a coil or electric         cables which are superconductors,     -   the device comprises several secondary cryocoolers,     -   the secondary cryocooler or one of the secondary cryocoolers is         in operation and contributes to the cooling of the member at the         same time as the main cryocooler,     -   the working fluid comprises or is made up of at least one out         of: helium, hydrogen, neon, nitrogen, argon, oxygen, methane,         krypton, xenon, CnHm, ammonium, a CFC, an HCFC, an HFC or any         other fluid refrigerant,     -   the fluid loop may use a buffer volume to limit the rise in         pressure of the loop when the system is at ambient temperature.

The invention also relates to a method for cooling a member to a low temperature using a cryogenic cooling device having any one of the features above or below, in which the main cryocooler is used to cool the member, the first chamber and the second chamber being placed under vacuum, the secondary cryocooler being selectively switched off or on while the main cryocooler is in operation.

Moreover, some embodiments of the invention may comprise one or more of the following features:

-   -   the main cryocooler is switched off and, at the same time as or         in anticipation of this, the secondary cryocooler is started in         order to cool the member, the third chamber being placed under         vacuum or kept under vacuum,     -   when a cryocooler is switched off, the cold head of the         cryocooler switched off is heated up to an ambient temperature         using at least one of the following steps: by spontaneous         natural heating, by commanded active heating, by forced         circulation of gas at ambient temperature into the chamber of         the cryocooler or around the exchangers via a coiled tube or any         other device, by bringing the volume of the cryocooler chamber         to atmospheric pressure,     -   the method comprises a step of repairing or maintaining one of         the two cryocoolers while the other cryocooler is in operation         and is cooling the member, the method comprising:     -   shutting down the cryocooler intended to undergo repair or         maintenance or keeping it in the switched off state,     -   keeping the cryocooler intended to undergo repair or maintenance         at ambient temperature or bringing it to ambient temperature,     -   opening the chamber containing the cryocooler intended to         undergo repair or maintenance,     -   dismantling the cryocooler intended to undergo repair or         maintenance so that it can be replaced or repaired without         connected the hermetic volume to the atmosphere,     -   maintaining the vacuum within the chamber of the other         cryocooler that is in operation and in the second chamber.

The invention may also relate to any alternative device or method comprising any combination of the features above or below.

Other particulars and advantages will become apparent on reading the following description, given with reference to the single FIGURE which is a schematic and partial view in cross section illustrating the structure and operation of a refrigeration device according to one possible embodiment of the invention.

With reference to the FIGURE, the cryogenic cooling device comprises a main cryocooler 18 comprising, in the conventional way, a cold head 19. The main cryocooler 18 (and in particular the cold head 19) is arranged in a first chamber 16 selectively placed under vacuum. The cold head 19 is equipped for example with a heat exchanger 17 to liquefy a working fluid. The exchanger 17 is, for example, screwed to the base of the cold head 19 using screws 20.

Underneath the cold head 19 and the exchanger 17, the main cryocooler 18 delimits a volume 21 for the liquefied working fluid, this volume being connected via two pipes, respectively an upper pipe 31 and a lower pipe 30, to a storage reservoir 9 for the liquefied working fluid.

This liquefied working fluid storage reservoir 9 contains the member 8 that is to be cooled by (direct or indirect) exchange of heat with the liquefied working fluid.

The storage reservoir 9 is housed in a second chamber 10 selectively placed under vacuum independently of the first chamber 16. What that means is that the pipes 30, 31 pass from the first 16 to the second 10 chamber through tubular portions 23 that connect the first 16 and second 10 chambers.

The second chamber 10 rests, for example, on the ground via a base and is, for example, sealed off at the top by a removable cover 11 (removable for example using screws 14).

The vacuums within the volumes of the first 16 and second 10 chambers are kept independent for example via one or more vacuum barriers 40 arranged respectively around the pipes 30, 31 inside the tubular connecting portions 23.

The vacuum barriers 40 may comprise any known system such as a double cone.

According to one advantageous feature, the device comprises a secondary cryocooler 1, for example of the same type as the main cryocooler 18. The secondary cryocooler 1 comprises a structure equivalent to the structure described hereinabove. What that means to say is that the cold head 7 of the secondary cryocooler 1 is arranged in a third chamber 4 selectively placed under vacuum. As before, the cold head 7 is equipped with a heat exchanger 2 for liquefying a working fluid. The exchanger 2 is screwed to the base of the cold head 7 using screws 5.

Underneath the cold head 7 and the exchanger, the secondary cryocooler 1 delimits a volume 121 for the liquefied working fluid, this volume 121 being connected by two pipes, respectively an upper pipe 131 and a lower pipe 130, to the same liquefied working fluid storage reservoir 9.

As before, the second chamber 10 is selectively placed under vacuum independently of the third chamber 4. The pipes 130, 131 pass from the third 4 to the second 10 chamber through the tubular portions 23 that connect the third 4 and second 10 chambers.

The vacuums within the volumes of the third 4 and second 10 chambers are kept independent via one or more vacuum barriers 40 arranged respectively around the pipes 130, 131, inside the tubular connecting portions 23.

In this way, the chambers 16, 10 and 4 are isolated from one another by vacuum barriers 40 so that the various chambers can be placed under vacuum independently of one another.

Where the working fluid is nitrogen, the device can be used to keep the member 8 at a cryogenic temperature (for example of 100 K).

The member 8 to be kept at a cryogenic temperature may, for example, be a superconductor coil, a heat exchanger in a heat exchange relationship with another heat-transfer fluid, or any other suitable member.

In one possible operation, the member 8 that is to be cooled is immersed in a bath of liquid nitrogen at a temperature of 100K for example.

The heat generated by the member 8 evaporates some of the liquid nitrogen from the bath 9. This gaseous nitrogen travels upward via the upper pipe 31 of the main cryocooler 18. On arriving at the exchanger 17 of the main cryocooler 18, the gaseous nitrogen is liquefied once again.

To do this, the exchanger 17 is kept at a temperature slightly below 100K by the cryocooler 18 which is in operation. The cold head 19 of the main cryocooler 18 extracts heat from the adjacent exchanger 17. The liquid nitrogen drops under gravity into the volume 21 situated under the exchanger 17 and then travels downward via the lower pipe 30 as far as the bath in the reservoir 9. This process takes place continuously in a working loop for the working fluid (nitrogen in this example).

A heater, for example an electric heater (not depicted) may be mounted on the heat exchanger 17 of the cold head 19 of the main cryocooler 18 to regulate the temperature thereof.

The secondary cryocooler 1 preferably has a structure and an operation identical to those of the main cryocooler 18.

The secondary cryocooler 1 is preferably used as a reserve. When the main cryocooler 18 is in operation, the secondary cryocooler 1 is switched off and the temperature of its cold head 7 is close to ambient temperature. The working fluid contained in the exchanger 2, the pipes 130, 131 is in the gaseous state.

As a result of thermal stratification, the gas in the pipes 130, 131 forms gaseous thermal plugs which limit transfers of heat between the secondary cryocooler 1 which is switched off and the reservoir 9.

By contrast, should the main cryocooler 18 fail or be switched off (for example for the purposes of carrying out maintenance on the main cryocooler 18), the secondary cryocooler 1 can be switched on, for example automatically.

After the main cryocooler 18 has been shut down, its cold head 19 and its exchanger 17 are warmed up to ambient temperature. This warming can be done either by waiting for them to warm up naturally, or by using an electric heater or by circulation of gas at ambient temperature, or by making the pressure in the first chamber 16 rise to atmospheric pressure.

The pressure in the first chamber 16 can be raised from the vacuum up to atmospheric pressure for example using a valve (not depicted) allowing selective communication between the interior volume of the chamber 16 and the exterior atmosphere.

The first 16 and the third 4 chambers are sealed off by at least one insulating and selectively removable cap 15 allowing direct access to the cryocooler, notably the cold head thereof.

For example, the first 16 and third 4 chambers are mechanically connected to the second chamber 10 and are raised up above the ground.

The removable cap 15 is, for example, positioned on the bottom part of each first 16 and third 4 chamber, so that it is adjacent to the cold head 19, 7.

Each cap 15 is, for example, mounted on the body of its chamber 16, 4 via fixing screws 22 or any other suitable system.

Thus, to gain access to the main cryocooler 18, the cap 15 is removed. The operator can then dismantle the exchanger 17, for example by removing the fixing screws 20 on the cold head 19. The flange 12 of the cryocooler 18 can then be disconnected from the chamber 16 (for example by removing the fixing screws 13). The cryocooler can then be taken out for replacement or maintenance thereof.

A new cryocooler or the repaired cryocooler can then be refitted. The flange 12 is once again fixed to the chamber 16. The fixing screws 20 which attach the exchanger 17 to the cold head 19 are refitted. The cap 15 is also put back into position.

A vacuum is once more created in the first chamber 16, for example by means of a vacuum pump and via a valve (neither of these has been depicted).

The repaired or exchanged main cryocooler 18 can then be switched on if the secondary cryocooler 1, which has now taken over the production of cold, malfunctions or requires maintenance.

The procedure for replacing or performing maintenance on the other cryocooler may be identical to the procedure described hereinabove.

The cryocoolers may for example operate on a Gifford MacMahon cycle. The cryocoolers 1, 18 can be insulated using a superinsulator of the multilayer or monolayer type. 

1-13. (canceled)
 14. A cryogenic cooling device comprising a main cryocooler with a cold head arranged in a first chamber placed under vacuum, a reservoir of working fluid arranged in a second chamber placed under vacuum, a member that is to be cooled being arranged in the reservoir in a heat exchange relationship with the working fluid, and a secondary cryocooler comprising a cold head arranged in a third chamber placed under vacuum, wherein: the cold head of the main cryocooler is thermally connected to a heat exchanger, itself fluidically connected to the reservoir via pipes forming a first circulation loop for the working fluid, the pipes passing from the first to the second chamber; the volumes under vacuum of the first and second chambers are independent which means to say that the vacuums in the first and second chambers are independent; the cold head of the secondary cryocooler is thermally connected to a heat exchanger, itself fluidically connected to the reservoir via pipes forming a second circulation loop for the working fluid; and the volume under vacuum of the third chamber is independent of the volumes under vacuum of the first and second chambers which means to say that the vacuums of the first, second and third chambers are independent.
 15. The device of claim 14, wherein at least one of the first and third chambers is sealed off by at least one selectively removable cap.
 16. The device of claim 15, wherein at least one selectively removable cap is arranged in the lower part of the chamber such that it is adjacent to the cold head.
 17. The device of claim 15, wherein at least one cap is mounted in a sealed fashion on the body of the chamber via fixing screws.
 18. The device of claim 14, further comprising, around the pipes passing from the first to the second chamber, vacuum barriers which separate the volumes under vacuum of the first and second chambers, the vacuum barriers being arranged in at least one tubular portion that connects the first and second chambers.
 19. The device of claim 14, further comprising, around the pipes passing from the third to the second chamber, vacuum barriers which separate the volumes under vacuum of the third and second chambers, the vacuum barriers being arranged in at least one tubular portion that connects the third and second chambers.
 20. The device of claim 14, wherein the cold head of the cryocooler(s) is associated with a heat exchanger that acts as a condenser for the working fluid.
 21. The device of claim 14, wherein the cold head of the main cryocooler is connected to the reservoir via two pipes the upstream ends of which are connected to a hermetic volume arranged under the cold head of the main cryocooler, the downstream ends of the pipes being connected to an upper end of the reservoir via a vertical or substantially vertical portion.
 22. The device of claim 14, wherein the cold head of the secondary cryocooler is connected to the reservoir via two pipes the upstream ends of which are connected to a hermetic volume arranged under the cold head of the secondary cryocooler and the downstream ends of which are connected to an upper end of the reservoir via a vertical or substantially vertical portion.
 23. A method for cooling a member to a low temperature using the cryogenic cooling device of claim 14, wherein the main cryocooler is used to cool the member, the first chamber and the second chamber are placed under vacuum and the secondary cryocooler is selectively switched off or on while the main cryocooler is in operation.
 24. The method of claim 23, wherein the main cryocooler is switched off, and at the same time or before the main cryocooler is switched off, the secondary cryocooler is started in order to cool the member, the third chamber being placed under vacuum or kept under vacuum.
 25. The method of claim 23, wherein when a cryocooler is switched off, the cold head of the cryocooler switched off is heated up to an ambient temperature using at least one of the following steps: spontaneous natural heating; by commanded active heating; by forced circulation of gas at ambient temperature into the chamber of the cryocooler or around the exchangers via a coiled tube or any other device; and by bringing the volume of the cryocooler chamber to atmospheric pressure.
 26. The method of claim 23, further comprising a step of repairing or maintaining one of the two cryocoolers while the other cryocooler is in operation and is cooling the member, the method comprising: shutting down the cryocooler intended to undergo repair or maintenance or keeping it in the switched off state; keeping the cryocooler intended to undergo repair or maintenance at ambient temperature or bringing it to ambient temperature; opening the chamber containing the cryocooler intended to undergo repair or maintenance; dismantling the cryocooler intended to undergo repair or maintenance so that it can be replaced or repaired without connected the hermetic volume to the atmosphere; and maintaining the vacuum within the chamber of the other cryocooler that is in operation and in the second chamber. 